After being harassed by their cat in the early sleeping hours, Instructables user 'briannaw' built a device whose purpose is to detect movement and make an annoying noise once detected. It is a simple, easy-to-build example using a motion detector, Arduino board and a buzzer fitted to a nicely-crafted enclosure, for example:

The success of this project will be predicated by the tenacity of a cat, so your "mileage may vary". Nevertheless, click here for the instructions and design notes. And for more, we're on twitter and Google+, so follow us for news and product updates as well.

It can be used as a noise-maker driven by your microcontroller for audible feedback of events, and it can also be used as a knock-detector input to sense events and react to them. Includes a built-in 1M resistor to allow the piezo element to detect shocks. For more information and to order, please visit the product page here.